A Study of Self-Heating Effects in Looped Carbon Nanotube Fibers

Recently, DallAgnol et al. [1] have studied the field electron emission (FE) characteristics of carbon nanotube (CNT)-based looped fibers and shown that these cathodes have very high effective field enhancement factors (FEFs). Based on SEM images taken after FE measurements from looped CNT fibers, they proposed a two-stage model for FE from these cathodes consisting of a looped fiber with CNT fibrils near its apex. The modeling of a combined two-stage structure (looped CNT fiber + fibrils) based on COMSOL simulations lead to apex FEF values in excellent agreement with an orthodoxy theory analysis [2]-[4] of FE experiments performed on these fibers. In this work, we perform extensive computational simulations of the temperature distribution through the fiber and in some of the fibrils near it apex, which are eventually responsible for their observed large FEFs. In order to determine the condictions for thermal runaway in these looped CNT two-stage emitters, we determined the temperature at the end of a fibril located at the apex of the fiber as a function of the fiber and fibril geometries, their electrical and thermal conductivities, and the distance between the apex of the fiber and the anode.